docs: def _compute_magnitude(self, rup, C):
          """
          Compute the first term of the equation described on p. 1144:
  
          ``c1 + c2 * (M - 6) + c3 * log(M / 6)``
          """
          return C['c1'] + C['c2'] * (rup.mag - 6.0) +\
              (C['c3'] * np.log(rup.mag / 6.0))